Transport tanks used to transport bulk quantities of food-grade liquids, such as by rail car or truck, normally incorporate vacuum breaker valves to allow atmospheric air to enter the tank if vacuum conditions develop therein. In this manner, the vacuum breaker valves prevent the tank from being damaged or destroyed by vacuum conditions in the tank such as by implosion.
Transport tank vacuum conditions can develop in a variety of different ways. For example, loading the tank with hot product can cause a vacuum condition to develop within the tank upon cooling of the product and air inside the tank. Localized pockets of vacuum pressure conditions can be generated during food product transport as the liquid in the tank is agitated in response to the acceleration or deceleration and the vibrations of the vehicle carrying the tank. Once product has reached its destination and is unloaded, atmospheric air must be allowed to replace discharged product as otherwise a tank vacuum condition can develop during unloading. After unloading a tank and before loading with product, the tank is normally cleaned with a fairly hot solution, typically at a temperature of approximately 190.degree. F. After cleaning the tank, the tank is closed and the cooling of the hot air in the tank generated from the cleaning process can cause a vacuum condition to develop in the tank.
One example of a commercially available vacuum breaker for use with transport tanks utilizes a spring-loaded valve stem with the spring normally biasing a vacuum plug to cover an off-center atmospheric air vent in the vent body. The vacuum plug is caused to move against the bias force of the spring when a vacuum develops in the tank allowing atmospheric air to enter through the vent into the interior of the tank.
During tank transport, the aforesaid vacuum breaker assembly may be caused to open even without the presence of a vacuum in the tank due to forces generated during transportation of the tank as when the vehicle transporting the tank accelerates and decelerates or rides over uneven surfaces such that the tank tends to vibrate causing the spring to compress opening the atmospheric air vent. Rough transportation conditions also cause liquid product to splash in the tank which, in combination with the opening of the valve assembly during transport, can cause product to spill out of the vent opening onto the exterior of the tank. This is particularly undesirable when food-grade liquids are being transported in that such product spillage creates the impression that the load has somehow been contaminated, in some instances causing the load to be rejected. Moreover, splashing of the product in the tank or other factors can dislodge the spring from the valve stem causing it to fall into the load, leaving the atmospheric vent open and the product exposed to contaminants from the exterior of the tank.
Thus, there is a need for a vacuum breaker valve assembly used with a tank for transporting bulk quantities of food-grade liquids which allows the flow of atmospheric air into the tank during vacuum conditions in the tank while also limiting leakage of product in the tank through the valve assembly to the exterior of the tank during transport of the tanks. Further, there is a need for a vacuum breaker valve assembly which achieves the above and also prevents splashing product from causing the valve spring to dislodge from the valve assembly and fall into the load.